1. Field of the Invention
The present invention generally relates to driving engines for watercraft, and, more particularly, engines for small watercraft that plane across the surface of the water.
2. Description of Related Art
Small planing watercraft, sometimes referred to as "personal watercraft," are typically configured with a bench seat that the driver and any passengers straddle while the driver grasps handlebars that are used to steer the watercraft. The engine is typically mounted in an engine compartment formed in a hull structure below a deck portion so that the output from the engine is transmitted directly, without a transmission, to a propulsion unit. At low engine RPM, and corresponding low velocity, the hull of the watercraft parts the water in what is referred to as a "non-planning" condition. As the engine speed and velocity of the watercraft increase, the watercraft bow rises until the watercraft crosses the so-called "hump" where the watercraft transitions from non-planing motion, where the hull splits the water, to planing motion where the hull skims over the surface of the water. Such small planing watercraft are typically equipped with high-speed, high-output engines which expel exhaust gases into the water at the stern of the watercraft and generally provide good mobility during planing motion. However, conventional high speed, high output watercraft engines have been found to produce insufficient power at lower engine speeds (RPM's) to enable the craft to move smoothly and quickly "over the hump" through the transition from non-planing to planing movement.